During a recording session, a sound engineer may receive direct feeds from instruments and/or position microphones among members of a band or other sources in order to receive sounds for recording. Using sound mastering equipment, the sound engineer may mix or adjust one or more of these input channels from which audio signals were received. In an example, the sound engineer may adjust individual audio signals to make the position of the singer be perceived by listeners to be in a central location when the recording is played through the loudspeakers of an audio system, a violin be perceived as to the left side of the singer, and a guitar be perceived as to the right side of the singer. These audio signals may be stored to an audio storage format for playback.
Audio systems may receive a stereo audio input signal, and develop more output channels than the received input channels. Such systems may distribute the audio input signal to the output channels based on analysis of aspects of one or more of the phasing, frequency, gain, correlation, harmonic content, harmonic decay, etc. of the audio input signals in the received channels with respect to one another. The process by which additional output channels are developed from the received input channels may be referred to as upmixing.